Introduction to the Modern Periodic Table of the Elements
The modern Periodic Table is made up of a series of rectangles.
Each rectangle provides us with four important pieces of imformation about an element:
(a) The symbol of the element.
(b) The name of the element1.
(c) The atomic number of the element.
(d) The atomic weight of the element2.
The elements are placed in the periodic table in order of increasing atomic number.
Horizontal rows of elements in the periodic table are known as periods.
Vertical columns of elements in the periodic table are known as groups.
Symbols of the Elements
The symbol of an element is made up of one or two letters3.
The first letter of the symbol is always a capital (upper case) letter.
If there is a second letter it is always a lower case letter.
The symbol for hydrogen is H not h
The symbol for helium is He not he and not hE and not HE
Names of the Elements
The name of the element is given under its symbol.
Under the symbol H is written the name of the element hydrogen.
Under the symbol He is written the name of the element helium.
Atomic Number of the Elements
The atomic number of the element is usually found above the symbol of the element in the periodic table.
The atomic number is always a whole number4
The atomic number of hydrogen is 1
The atomic number for helium is 2
The atomic number of an element tells us the number of protons in the nucleus of an atom or ion of the element.
Example: hydrogen has atomic number 1, there is 1 proton in the nucleus of a hydrogen atom or ion
Example: helium has atomic number 2, there are 2 protons in the nucleus of a helium atom
Atomic Weight of the Elements
The atomic weight of the element is usually shown below the symbol of the element.
It is given as a decimal number without units of measurement5
The atomic weight of hydrogen is 1.008
The atomic weight of helium is 4.003
If the atomic weight is in brackets, the element has only very short-lived isotopes and it has not been possible to determine the atomic weight of the element. The number in brackets is the atomic mass for the most common isotope (isotopic mass).
The atomic weight of the most common radioactive isotope of radon is 222.0
Periods of the Periodic Table
In the modern periodic table, the rectangles containing the information about the elements are arranged in order of increasing atomic number as you read from left to right.
3 Li lthium 6.941
4 Be beryllium 9.012
5 B boron 10.81
6 C caron 12.01
7 N nitrogen 14.01
8 O oxygen 16.00
9 F fluorine 19.00
10 Ne neon 20.18
These rows of elements in the periodic table are known as Periods.
Each period in the periodic table has been assigned a number.
Period 1 →
Period 2 →
Period 3 →
Period 4 →
Period 5 →
Period 6 →
Period 7 →
The elements hydrogen (H) and helium (He) make up the first period in the periodic table, Period 1.
The elements lithium (Li) to neon (Ne) shown above make up the second period of the periodic table, Period 2.
Groups of the Periodic Table
The periods containing the elements are stacked on top of each other to form vertical columns which are known as Groups.
Each group in the periodic table has been assigned a number between 1 and 18.
The groups are numbered sequentially from left (group 1) to right (group 18).
Group 1 ↓
Group 2 ↓
Group 3 ↓
Group 4 ↓
Group 5 ↓
Group 6 ↓
Group 7 ↓
Group 8 ↓
Group 9 ↓
Group 10 ↓
Group 11 ↓
Group 12 ↓
Group 13 ↓
Group 14 ↓
Group 15 ↓
Group 16 ↓
Group 17 ↓
Group 18 ↓
The elements helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn) make up a group in the periodic table.
Group 18 contains the elements helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn).
Some groups have also been given names:
Group 1 is also known as the alkali metals
Group 2 is also known as the alkaline earth metals (or alkaline-earth metals)
Group 16 is also known as the chalcogens
Group 17 is also known as the halogens
Group 18 is also known as the noble gases (sometimes also referred to as the inert gases)
2 He helium 4.003
10 Ne neon 20.18
18 Ar argon 39.95
36 Kr krypton 83.80
54 Xe xenon 131.3
86 Rn radon [222.0]
The Modern Periodic Table of the Elements
The colour of the boxes in the periodic table below shows the standard state of the element (25oC and 1 atmosphere pressure)
Solid elements are found in green boxes.
Most of the elements are solids.
Liquid elements are found in lemon boxes.
There are two liquid elements; mercury and bromine
Gaseous elements are found in blue boxes.
There are eleven gaseous elements; hydrogen, helium, nitrogen, oxygen, fluorine, neon, chlorine, argon, krypton, xenon, and radon.
The colour of the text in the boxes of the periodic table below shows the metallic character of the element:
Metallic elements are written in black text.
Most of the elements are metals.
Non-metallic elements are written in red text.
All the non-metallic elements are found on the right hand side of the periodic table (except for hydrogen).
Semi-metals or metalloids are written in orange text.
Semi-metals lie between the metals on the left and the non-metals on the right of the periodic table.
Download the most recent version of the Periodic Table at IUPAC
1The IUPAC recognizes the commonly used alternative spellings for two elements:
The element with atomic number 13 and symbol Al may be spelt as aluminium or as aluminum.
The element with atomic number 55 and symbol Cs may be spelt as caesium or as cesium.
BUT it should be noted that these elements are present in the IUPAC periodic table as caesium and aluminium.
2The IUPAC periodic table uses standard atomic weights and provides the lower and upper bounds of the standard atomic weight for some elements. Debate still rages about whether the term atomic mass, atomic weight, relative atomic mass, relative atomic weight, or standard atomic weight should be used. Don't worry about it, at High School you can treat all these terms as meaning the same thing.
3The exception to this is for elements that have not yet been discovered. These elements are assigned a name based on their atomic number which will have three numbers, so the symbol for these elements has three letters. Once the element has been produced, it will be officially named and given an official symbol. If you are interested in this topic, you can found out more in the September 2012 issue of AUS-e-NEWS.
4A whole number is a counting or natural number, it does not include negative numbers, nor numbers which are fractions or decimals etc.
5Prior to 1961 the unit amu (atomic mass unit) was used. Since then the unit u (unified atomic mass unit) or Da (dalton) have been widely used but neither of these is an SI unit (as defined by the CIPM, International Committee for Weights and Measures). The issue will be further complicated if the dalton is redfined as being 0.001/NA kg since it would no longer be a unit of atomic mass relative to carbon-12. For High School students it is probably best to avoid the problems and use relative atomic mass as a quantity with no units.
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